Composite bearing with double ball bearings, process for its assembly and tool for the realization of a pair of collars of said bearing

ABSTRACT

Composite bearing with double ball bearings ( 4 ) for the rotary support of a rotating shaft ( 1 ) of a very high precision device, wherein this bearing with double ball bearings is constituted by the juxtaposition of two bearings with single ball bearings having two respective corresponding collars ( 5   1   , 5   2 ), interior or exterior, tightened axially against one another with a predetermined pre-stress, characterized in that the two collars ( 5   1   , 5   2 ) maintained tightened against one another with said pre-determined pre-stress are soldered ( 9 ) to each other by their co-operating faces.

FIELD OF THE INVENTION

[0001] The present invention relates to improvements made in the fieldof composite bearings with double ball bearings for the rotary supportof a rotating shaft of a very high precision device, wherein thesebearings with double ball bearings are constituted by the juxtapositionof two bearings with single ball bearings having two respectivecorresponding collars, interior or exterior, fitting tightly axially oneagainst the other with predetermined pre-stress.

DESCRIPTION OF THE PRIOR ART

[0002] In some very high precision devices (for example in inertialnavigation centers), it is necessary and indispensable that a rotatingshaft is mounted and supported in a bore with very great precision ofcoaxiality without any play, in order to obtain high performances. Sucha requirement necessitates that the balls of the ball bearings remainpermanently in the contact of their path in order to avoid theconsequences inherent in “take-offs” of the balls (generation of shocks,wear and tear, appearance of plays) , which are eventually reflected bya loss of precision of the device. In order to clarify ideas, it will benoted that in the case of the appearance of a vibratory operatingregime, it is an effort which can for example reach 900 N which can beexerted on a ball bearing collar having a diameter of the order of 35 mmand a thickness of around 3 mm.

[0003] In order to be able to meet practical requirements, one thusresorts to bearings equipped not with single ball bearings, but withdouble ball bearings.

[0004] The easiest solution, which would consist in using a singlebearing equipped with double juxtaposed ball bearings, however, cannotbe used. This is because, even if very high precision machinery wereused, the double ball bearings have dimensional differences (distancebetween axes, diameters of the balls, diameter of the receptacles,etc.), which are too great for the rotating shaft to be able to besupported in the bore with all the required precision and absence ofplay.

[0005] Thus it is known that one can resort to two bearings with singleball bearings, which are paired and which are then implemented underaxial pre-stress of their respective corresponding collars, eitherinterior or exterior, in such a way that they thus behave like a singlebearing with double ball bearings. In this case, as opposed to thesingle bearing with double ball bearings, each bearing can bemanufactured with all the desired precision. The respective co-operatingfaces of the two collars, interior or exterior, of the two bearings canbe rectified in order to be in perfect contact one against the other.Also, the rigidity conferred by the pre-stressing finally leads to abearing (hereinafter referred to as “composite bearing” because it isconstituted by the reunion of two bearings with mono-ball bearings),which can satisfy practical requirements with regard to precision andthe absence of play of the assembly of the rotating shaft in the supportbore.

[0006] Even if the results obtained with this type of composite bearingsatisfy practical requirements, on the other hand the assembly processesof such a composite bearing are complex and present many problems.

[0007] A usual assembly process takes place as follows. After pairing ofthe composing pieces (and in particular of the two collars to be placedside by side under pre-stress), the two bearings are dismounted, then afirst collar is implemented in support against an axial capacity; forexample in the case of an interior collar, it is mounted on the shaftjust to the point of abutment against a radial, annular retaining wallprovided on the shaft.

[0008] The second collar is then pre-positioned in immediate proximityto the first collar, but without being in contact with it; in theexample considered of interior collars, the second collar is mounted inturn on the shaft just to immediate proximity of the first collar.

[0009] One thus brings an axial pressure tool against the second collarand, with the assistance of this tool, one displaces the second collaraxially towards the first collar just to the point of physical contactwith it, then one continues to exert an effort on the second collaruntil the support pre-stress of the second collar on the first reaches apre-determined value. Still within the scope of the considered exampleof interior collars, the tightening tool can consist in a nut which isscrewed on the end of the shaft, which is threaded to this effect. Thisnut, which is moreover appropriately suited to be in perfect axialsupport against the second collar, is suitable, in the course of itsrotation, for displacing the second collar to first of all take itagainst the first collar, then for putting the two collars under axialpre-stress at a pre-determined value.

[0010] The drawbacks of this existing process consist in that it isnecessary on the one hand to specifically adjust (threading for thetightening nut) the support element of the collars under pre-stress (thesupport bore for exterior collars, the shaft for interior collars) andon the other hand it is necessary to maintain in permanence the elementsnecessary for the assembly (threading and nut), since the pre-stress ofthe collars is only due to the presence of the tightening tool (nutscrewed on the threading for example). This results in an increase inweight of the unit and, in the case of interior collars, an inertialmodification of the mobile gear. These constraints may not be accepted,in particular when it is a matter of reducing as far as possible thedimensions of the device thus equipped and reducing the weight thereof,as well as when it is a matter of increasing the response rapidityperformances by reducing in a maximum way the inertias of the mobileorgans.

[0011] In order to attempt to overcome said drawbacks, one has proposedthe combining of the second collar, in support under pre-determinedpre-stress against the first collar, by sticking (by a resin film) thesecond collar on its support. In this case, it is admittedly stillnecessary to resort to a tightening tool to place the second collar andthe first side by side and to exert the pre-stress until the sticking ofthe second collar on its support is mechanically effective. However, thetightening tool can then be withdrawn, and it is no longer present inthe completed device which is ready to function.

[0012] However, this process itself also has drawbacks. Firstly, even ifthe tightening tool is admittedly not maintained in the device, certainadjustments necessary to its use remain in place: thus, in the case of anut suitable for pushing the second collar, the threading realizedeither in the bore (for exterior collars) or on the end of the shaft(for interior collars) remains on the bore or on the shaft. Practice maynot accept the presence of this adjustment, which is not necessary tothe functioning of the device.

[0013] In particular, the sticking film for combining the second collar,which is relatively thin (for example typically 1.5 μm), is not veryresistant to thermal shocks (for example typically variation of 3 to 4°C. per second in an ambiance of around 70° C.). The sticking filmfractures and the collars are no longer maintained under pre-stress(even becoming unstuck from their support), in such a way that the shaftis no longer supported with the required precision and the device losesits precision, or is even no longer in a state of being able tofunction.

[0014] In order to attempt to overcome these drawbacks, it has beenproposed to increase the thickness of the layer of glue, which thusbecomes able to withstand severe thermal conditions withoutdeterioration. However, due to the very reason of the thickness of thelayer of glue, the rigorous coaxiality of the collars and of the supportcan no longer be assured when the collars are put in place on thesupport. It is thus necessary to conserve axial positioning zones(without glue), which are suitable for assuring the mutual axialmaintenance of the collars and of the support and of the axial zones ofdifferent diameter (with glue), which are suitable for making thecollars solid with the support.

[0015] Such an assembly process necessitates manufacturing processes andproves to be too complicated.

[0016] Besides, it is to be noted that all the processes which have justbeen explained have the additional drawback that the pre-stressing ofthe two collars takes place during the very course of the assembly ofthe second collar on the support (bore or shaft), which particularlycomplicates the operational mode of pre-stressing.

[0017] From this viewpoint, it is thus desirable for the two collars tobe able to be reunited under axial pre-stress before their assembly,then to be mounted on the support in the form of a unitary block, whichcan thus be put into place in the same way as a traditional bearing withdouble ball bearings.

[0018] With this aim in view, one could admittedly envisage making thetwo collars solid with the assistance of crimping tongs. However, thisprocess does not prove to be very practical, and furthermore theassembled collars would remain equipped with the crimping tongs, whichmaintain the pre-stress. This is again one of the drawbacks of the firstprocess explained above.

SUMMARY OF THE INVENTION

[0019] It is thus an object of the invention to overcome as far aspossible the drawbacks presented by the different solutions as in thestate of technology and to propose an improved original solution whichallows pre-assembly of the collars under pre-stress, which dismisses anyadaptation of the support specifically for the mounting of the collars,which does not allow to remain in the completed device any additionalorgan specific to the mounting and/or to the maintenance of thepre-stress of the collars, and which allows production in relativelylarge series of collars which are pre-assembled under pre-stress

[0020] For this purpose, according to a first embodiment, the inventionproposes a composite bearing with double ball bearings such as thatmentioned in the introductory clause which according to the invention ischaracterized in that the two collars maintained fitting tightly oneagainst the other with said pre-determined pre-stress are soldered toone another by their co-operating faces.

[0021] According to a preferred embodiment, at least one of the edges,exterior or interior, of the co-operating faces of the collars isbeveled, and these beveled edges together form an annular groove. Thesoldered joint is situated at the bottom of the groove and the solderedjoint does not project outside the groove.

[0022] Advantageously, it is the exterior edges of the co-operatingfaces of the collars that are beveled in order to define an exteriorgroove and the collars are made solid by a soldered joint extendingalong the exterior edges of the faces joined end to end of the twocollars. However, it is also possible for the interior edges of theco-operating faces of the collars to be beveled in order to define aninterior groove and for the collars to also be made solid by a solderedjoint extending along the interior edges of the faces joined end to end.Preferably, the two collars are soldered on the interior and on theexterior.

[0023] The soldered joint can be formed from successive, continuous ordiscontinuous sections, on the perimeter of the groove, wherein thesoldered joint can in practice advantageously be a laser soldered joint.

[0024] According to a second embodiment, the invention proposes aprocess for assembling a bearing with double ball bearings for therotary support of a rotating shaft of a very high precision device,wherein this bearing with double ball bearings is constituted by thejuxtaposition of two bearings with single ball bearings having two oftheir respective collars, interior or exterior, axially fitting tightlytogether, wherein this process according to the invention ischaracterized in that it consists of the series of the following stages:

[0025] one pairs two bearings with single ball bearings, wherein theirrespective collars, interior or exterior, have co-operating faces withcomplementary geometric properties,

[0026] after dismounting of the two bearings, one positions said tworespective collars against one another, and one tightens them axiallyagainst one another with a pre-determined pre-stress,

[0027] soldering is carried out along at least one of the edges,exterior or interior, of the co-operating faces of the two respectivecollars maintained under pre-stress, in such a way that the solderedjoint does not project radially beyond the peripheral annular faces ofsaid collars,

[0028] then one re-assembles the one-piece component formed from the twosoldered under pre-stress collars in position on its support organ andone finishes the complete assembly of the bearing by excentrationaccording to the principle of deep-groove ball bearings.

[0029] In a simple way, one solders the two collars along the exterioredges of their co-operating faces. However, in order to homogenize theefforts being exerted between the two collars, it is likewise desirableto also solder the two collars along the interior edges of theircooperating faces

[0030] In practice, the soldering is achieved with the assistance of alaser beam. In the case of soldering on the interior edges of thecollars, the laser beam is guided onto the interior edges of theco-operating faces of the collars successively through lights of acomponent for support and centering of the collars positioned withinthem, and the soldering is carried out in successive sections. By reasonof the passage of the laser beam through said lights, the laser beamcannot be displaced in a continuous way, which means that the solderingis realized by discontinuous, successive sections.

[0031] Preferably, the edges of the respective collars are beveled andthe soldering is effected in the bottom of the groove formed by twoco-operating beveled edges, in such a way that no soldered joint elementprojects and the peripheral lateral face of the assembled collarsremains smooth. Nothing hampers their assembly on the support (bore orshaft).

[0032] Advantageously, the two collars being soldered along theirinterior and exterior co-operating edges, the soldering of the interiorco-operating edges is effected firstly and the soldering of the exteriorco-operating edges secondly.

[0033] According to a third embodiment, the invention proposes a tool ofsupport, of coaxial centering and of pre-stressing of two collars ofball bearings destined to be soldered to one another, in order toimplement said process.

[0034] According to a first method of realization, a tool designed tohandle two interior collars is proposed, wherein this tool, beingconstructed according to the invention, is characterized in that itcomprises

[0035] an essentially tubular chuck having a lateral wall with acylindrical external face of revolution, which is suitable forsupporting and centering coaxially, by their internal faces, twointerior collars positioned one after the other,

[0036] first solid means of axial abutment of said chuck, against whicha free face of one of the two collars comes in support,

[0037] and coaxial means of tightening to said chuck, comprising secondmeans of axial abutment which are suitable for coming in support againstthe free face of the other of the two collars in such a way that underthe effect of said tightening means, the two collars are tightenedagainst one another until a pre-determined pre-stress value is obtained.

[0038] Advantageously in this case, the tool comprises a support plateof the chuck, wherein said plate is in the form of a bowl suitable forreceiving coaxially a hub. The first means of abutment are provided onor constituted by the peripheral edge of the lateral wall of said hub.The second means of abutment are provided on a solid cover of saidchuck, wherein said cover is open centrally to give access to theinterior of the chuck.

[0039] In a second method of realization of the tool, a tool designed tohandle two exterior collars is proposed, wherein this tool, beingconstituted according to the invention, is characterized in that itcomprises:

[0040] a hub of which the lateral wall presents a cylindrical internalface of revolution suitable for supporting and centering axially, bytheir external faces, two exterior collars positioned one after theother, wherein the lateral wall of said hub is provided with amultiplicity of traversing lights distributed peripherally and inrelation to which the external edges to be soldered of the two collarsare situated, wherein each light constitutes a passage so that a laserbeam crossing it can solder said external edges of the two collars,

[0041] an approximately tubular chuck supported at the interior of thehub and having a lateral wall situated in relation to the wall of thehub,

[0042] first solid means of axial abutment of said hub, against which afree face of one of the two collars comes in support,

[0043] and coaxial means of tightening to said hub, comprising secondmeans of axial abutment suitable for coming in support against the freeface of the other of the two collars, in such a way that under theeffect of said means of tightening, the two collars are tightenedagainst one another until a pre-determined pre-stress value is obtained.

[0044] Advantageously in this case, the second means of abutment aresolid in respect of the chuck and are constituted by a flank projectingradially towards the exterior from the upper edge of the lateral wall ofsaid chuck.

[0045] Advantageously, the tool has means of rotary support of thechuck.

[0046] Preferably, in one or the other of said tools, the lateral wallof the chuck is equipped with a multiplicity of traversing lightsdistributed peripherally and in relation to which the edges,respectively interior and exterior, of the co-operating faces of the twocollars to be soldered are situated, wherein each light constitutes apassage so that a laser beam crossing it can solder the edges of thecollars appearing at the opening of this passage. It is thus desirablefor the lights of the chuck to be inclined towards the foot of theinterior towards the exterior of the chuck wall in order to facilitatethe positioning of the soldering laser beam approximately in the axis ofeach light.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The invention will be better understood upon reading thefollowing detailed description of certain preferred modes of realizationgiven solely by way of example, being in no way limitative. In thisdescription, reference is made to the attached drawings in which:

[0048]FIG. 1 is a partial schematic view in section of a unitconstituted by a rotating shaft supported in a bore through theintermediary of a bearing with double ball bearings constructedaccording to the invention;

[0049]FIG. 2 is a partial schematic view in section, on a larger scale,of a one-piece component formed from two collars soldered to each otheraccording to the invention in order to equip the bearing of FIG. 1;

[0050]FIG. 3 is a partial schematic view in section of an alternativeembodiment of the assembly of FIG. 1; and

[0051]FIGS. 4 and 5 are views in section of a tool constructed accordingto the invention for the realization of double collars, respectivelyinterior and exterior.

DETAILED DESCRIPTION OF THE INVENTION

[0052] Referring first of all to FIG. 1, a rotating shaft 1, included ina very high precision device (for example a gyrometer of a navigationinertial centre) is supported in rotation in a bore 2 of a support body3 through the intermediary of a bearing 4 with double ball bearings.

[0053] The bearing 4 with double ball bearings is constituted by thejuxtaposition of two bearings with single ball bearings. In the exampleshown, it is constituted by the juxtaposition of two interior collars 5₁ and 5 ₂ (that is to say mounted on the shaft 1) , which respectivelyretain two annular rows of balls 6 ₁ and 6 ₂ in relation respectivelywith two exterior collars 7 ₁ and 7 ₂ (that is to say mounted in thebore 3). The details of the construction of the balls with separationcasing and other organs known by specialists is not shown, in order toavoid complicating the drawing.

[0054] In order that the bearing 4 with double ball bearings with doublecollar (hereinafter referred to as “composite bearing”) has the samemechanical rigidity characteristics as a one-piece bearing with doubleball bearings, two of the collars, for example the two interior collars5 ₁ and 5 ₂, are maintained side by side under a pre-stress of apre-determined value.

[0055] In order to avoid the drawbacks shown by the previous methods ofassembly which were explained above, it is provided according to theinvention that the two interior collars 5 ₁ and 5 ₂ are soldered to oneanother by their co-operating faces, wherein the soldering is effectedwhile the two collars are maintained against one another under saidpre-stress of the pre-determined value.

[0056] Considerable advantages are thus obtained from this type ofassembly according to the invention. Thus, once they are soldered, thetwo collars are mechanically solid in respect of one another and form aone-piece component which is particularly rigid by reason of thepre-stress under which the making solid by soldering has been carriedout. In addition, the mechanical resistance of the soldered joint issuch that it does not run the risk of being destroyed under the effectof the pre-stress.

[0057] Thus, it becomes possible to make the two collars solid inrespect of one another in the required conditions before their assemblyon the shaft and, only once the collars are made solid, the one-piececomponent is mounted on the shaft. This results in a greatsimplification of the assembly (one single instrument to be mountedinstead of two), and in particular all the exterior means which weredestined to the maintenance of the pre-stress (nut-threading, glue,etc.) are no longer needed. The shaft no longer has to be manufacturedin a specific way, the weight of the rotating unit is minimum and itsinertia is reduced.

[0058] In other words, owing to the means provided by the invention, themanufacture and assembly of the unit are simplified and the operatingproperties of this unit are improved at the same time.

[0059] In practical terms, as is visible in FIG. 1, but is even morevisible in FIG. 2, at least one of the edges, exterior and/or interior,of the co-operating faces of the two collars 5 ₁ et 5 ₂ is beveled.These beveled edges together form, once the two collars are placed sideby side, an annular groove 8. With the beveled edges being, in thesimplest way, a simple annular dish, the groove 8 thus constitutedpresents a transversal section in a V. The soldered joint 9 is thusdeposited in said groove 8 in such a way that no part of the solderedjoint projects out of the groove 8. The groove 8 must therefore havegeometry (deepness, opening) which is able to deal with a solderingcordon suitable for assuring the required mechanical assembly, withoutexterior projection, in order to avoid hampering the subsequent assemblyof the double collar.

[0060] It is understood that the realization of the soldering is easierwhen it is the exterior edges of the co-operating faces of the collarswhich are beveled and when the groove 8 opens onto the exterior.

[0061] However, both for reinforcing the mechanical assembly of the twocollars by not leaving this function to one single soldering cordon andfor avoiding certain difficulties which arise during pre-stressing ofthe collars for an exclusively exterior soldered joint (risk oftipping-over of the two collars under the effect of the effort ofpre-stressing), it proves advantageous for soldering to be also carriedout along the interior edges of the co-operating faces of the collarsand thus for these interior edges themselves also to be beveled. Underthese circumstances, in order to avoid said risk of tipping-over duringpre-stressing, the interior soldering should be carried out first andthen, only after this, should the exterior soldering be carried out.

[0062]FIGS. 1 and 2 show the two interior collars 5 ₁ et 5 ₂ made solidby two soldered joints 9, interior and exterior.

[0063] The soldering is advantageously carried out by laser, accordingto the techniques known by experts. The soldering cordon can be realizedin a continuous way, in particular for the exterior soldered joint, forexample when one can make the unit of the two pre-stressed collars turncontinuously in front of the laser beam.

[0064] However, it is not excluded that the soldering is carried out bysuccessive sections, in order to form either a continuous solderingcordon by joined-up sections or a discontinuous soldering cordon. Such aprocess of soldering by successive sections is in particular implementedfor the interior soldering by reason of the difficulty of access to theinterior groove 8, and a specific tool will be presented below in orderto facilitate this work.

[0065] The preceding explanations have been given more specifically withregard to the mode of realization illustrated in FIGS. 1 and 2, in whichthe two collars 5 ₁ and 5 ₂ are interior collars, that is to say thosewhich are solid in respect of the rotating shaft 1.

[0066] However, it is clear that the provisions of the invention alsoapply in the same way and with the same advantages to exterior collars,that is to say the collars 7 ₁ et 7 ₂ which are solid in respect of thebore 2 of the support body 3, as is illustrated in FIG. 3, wherein thesame numeric references are retained for the components identical tothose of FIGS. 1 and 2.

[0067] Thus, for the assembly of a bearing with double ball bearings forthe rotary support of a rotating shaft of a very high precision device,wherein this bearing with double ball bearings is constituted by thejuxtaposition of two bearings with single ball bearings having two oftheir respective collars, interior or exterior, tightened axiallyagainst one another, according to the invention the following process isfollowed:

[0068] one pairs two bearings with single ball bearings; in particularthus, their respective collars, interior 5 ₁ and 5 ₂ or exterior 7 ₁ and7 ₂, have co-operating faces having complementary geometric properties;

[0069] after dismounting of the two bearings, one positions said tworespective collars, 5 ₁, 5 ₂ or 7 ₁, 7 ₂ against one another and onetightens them axially against one another with a pre-determinedpre-stress;

[0070] one then carries out soldering along at least one of the edges,interior or exterior, of the cooperating faces of the two respectivecollars maintained under said pre-stress, in such a way that thesoldered joint does not radially project beyond the peripheral annularfaces of said collars, wherein said soldered joint is carried out onlyalong exterior edges or else along interior edges first of all, thenoutside of their cooperating faces, preferably by implementation of alaser beam;

[0071] then one mounts the one-piece component formed from the twocollars soldered to one another, under pre-stress, in position on itssupport organ and one finishes the complete assembly of the bearing byexcentration according to the principle of deep-groove ball bearings.

[0072] For the implementation of the soldering process of the twocollars maintained under pre-stress, according to the invention aspecific tool is proposed, of which two modes of realization are shownin section in FIGS. 4 and 5 respectively. This tool achieves thesupport, the coaxial centering and the pre-stressing of two collars ofball bearings in order to be able to solder them to one another, whilethey are maintained under pre-stress, along the interior and/or exterioredges of their co-operating faces.

[0073] In FIG. 4, the tool designated in its entirety by the reference10 is designed for soldering two interior collars 5 ₁, 5 ₂ maintainedunder pre-stress. The tool 1 comprises a plate 11 having, above, a bowl12 suitable for retaining coaxially a chuck 13 which is essentiallytubular and has a lateral wall 14 with a cylindrical external face ofrevolution which is able to support and to center coaxially two collars5 ₁ and 5 ₂ positioned one after the other. Additionally provided arefirst means of axial abutment 15, solid in respect of said chuck,against which a free side of one of the collars 5 ₁ comes in support.

[0074] As shown in FIG. 4, the first means of abutment 15 can be carriedby a hub 16, which rests in said bowl 12 of the plate 11 and which isdesigned in a bowl in which said chuck 13 is fitted in. It is thus theupper annular edge of the lateral wall of said hub 16, which has anexternal diameter which is appreciably greater than the externaldiameter of said chuck, which constitutes said first means of abutment15.

[0075] On the upper edge of the chuck 13, a component in the form of acover 17 is made solid, of which the lateral skirt 18 surrounds, at aradial distance, the two collars 5 ₁, 5 ₂ and is maintained coaxially byan excrescence of the hub 16. The plateau 19 of the cover 17, or else asshown here a ring solid in the interior of the said plateau 19,constitutes second means of abutment suitable for bringing to bearagainst the free face of the other collar 5 ₂ when the chuck 13 isaxially brought closer to the hub 16.

[0076] In order to ensure this bringing-closer, a tightening instrumentsuch as a bolt 21 positioned coaxially to its head which takes supportagainst the lower face of the hub 16 and its stem, which crosses thebottom of said hub, is screwed into the bottom of the chuck 13. Thetightening of the bolt 21 enables the two collars 5 ₁, 5 ₂ to besubjected to a pre-determinable pre-stress.

[0077] In addition, one or several pieces 22 are engaged in alignedbores of the support surface 11, of the hub 16 and of the chuck 13 inorder to make them solid in rotation.

[0078] In order that the collars 5 ₁, 5 ₂ can be soldered to one anotheralong the interior edges of their co-operating faces by means of a laserbeam, the chuck 13 and the cover 17 are constructed as follows.

[0079] The cover 17 is open in 23 in its central region.

[0080] The chuck 13 is hollowed out centrally in a bowl in 24 and itslateral wall 25 is pierced with a multiplicity of traversing lights 26distributed peripherally in a regular way and emerging in regard to thejoined-up faces of the two collars 5 ₁, 5 ₂. These lights 26 areinclined towards the bottom radially from the interior towards theexterior.

[0081] Thus a laser beam can be guided through the opening 23 of thecover and successively through all the lights 26 in the axis thereof, inorder to achieve discontinuous soldering cordons on the interior edgesof the co-operating faces of the collars 5 ₁, 5 ₂ while these collarsare maintained under pre-determined axial pre-stress by tightening ofthe hub and of the chuck.

[0082] In order to facilitate the work which has just been described,with the laser source being positioned in a fixed way, the chuck 13 isturned around its axis so that all the lights 26 are successivelypresented to the laser beam. For this purpose, the plate 11 isconstructed to be supported in a rotary way (means not shown,schematized by the arrow 27).

[0083] As for the realization of the soldering of the exterior edges ofthe co-operating faces of the collars 5 ₁, 5 ₂, this can be realizedusing the tool 10 in providing lights (not shown) in the skirt 18 inorder to obtain discontinuous access to the laser beam. However, thissoldering can also be realized, after extraction of the one-piececomponent formed by the two collars 5 ₁, 5 ₂ soldered in the interior,by positioning this one-piece component on another support, in such away that the exterior soldering can be carried out either in adiscontinuous way or in a continuous way on the whole periphery.

[0084] In FIG. 5, a further mode of realization of the tool isillustrated, wherein the tool is designated in its entirety by thereference 28 and is constructed for the soldering of two exteriorcollars 7 ₁ and 7 ₂. The general design of the tool 28 remains identicalas a whole to that of the tool 10 of FIG. 4, with the exception that itis adapted so that the exterior collars 7 ₁, 7 ₂ are supported andcentered coaxially by their internal faces.

[0085] For this purpose, the hub 16 presents a lateral wall 29 extendedtowards the top, above and radially shifted towards the exterior inrelation to said retaining wall 15 of support. It is against the face30, turned towards the interior, of this wall 29 that the collars 7 ₁, 7₂ are in support, being distanced radially from the lateral wall 14 ofthe chuck 13.

[0086] The lateral wall 29 of the hub 16 is pierced by a multiplicity oflights 31 distributed over the perimeter of said wall 29. These lights31, approximately radial, emerge approximately in regard to the exterioredges of the co-operating faces of the two exterior collars 7 ₁, 7 ₂thus becomes possible to carry out the exterior (discontinuous)soldering of the collars 7 ₁, 7 ₂ by guiding a laser beam (arrow 32)successively through the lights 31.

[0087] As for the lateral wall 14 of the hub 16, it is extended radiallytowards the exterior, along its upper edge, by an annular radial flank33, which extends at least to just above the site of the collars 7 ₁, 7₂. Thus, in rotating the bolt 21, one brings the chuck 13 closer to thehub 16 and the two collars 7 ₁, 7 ₂ are brought tightly together andpre-stressed between the annular flank 33 and the retaining wall 15.

[0088] The lateral wall 14 of the chuck 13 retains said lights 26,through which a laser beam can be guided (arrow 34) in order to reachand solder (in a discontinuous way) the internal edges of theco-operating faces of the two collars 7 ₁, 7 ₂.

1. A composite bearing with double ball bearings for the rotary supportof a rotating shaft of a very high precision device, wherein thisbearing with double ball bearings is constituted by the juxtaposition oftwo bearings with single ball bearings having two respectivecorresponding collars, interior or exterior, tightened axially againstone another with a pre-determined pre-stress, wherein the two collarsmaintained tightened one against the other with said predeterminedpre-stress are soldered to one another by their co-operating faces. 2.The bearing according to claim 1 , wherein at least one of the edges,exterior or interior, of the co-operating faces of the collars isbeveled and these beveled edges together form an annular groove, whereinthe soldered joint is situated at the bottom of the groove, and whereinthe soldered joint does not project outside of the groove.
 3. Thebearing according to claim 2 , wherein it is the exterior edges of thecooperating faces of the collars which are beveled in order to define anexterior groove, and wherein the collars are made solid by a solderedjoint extending along the exterior edges of the joined-up faces.
 4. Thebearing according to claim 2 , wherein it is the exterior edges of thecooperating faces of the collars which are beveled in order to define anexterior groove, wherein the collars are made solid by a soldered jointextending along the exterior edges of the joined-up faces, wherein theinterior edges of the co-operating faces of the collars are beveled inorder to define an interior groove, and wherein the collars are alsomade solid by a soldered joint extending along the interior edges of thejoined-up faces.
 5. The bearing according to claim 2 , wherein it is theexterior edges of the cooperating faces of the collars which are beveledin order to define an exterior groove, wherein the collars are madesolid by a soldered joint extending along the exterior edges of thejoined-up faces, wherein the interior edges of the co-operating faces ofthe collars are beveled in order to define an interior groove, whereinthe collars are also made solid by a soldered joint extending along theinterior edges of the joined-up faces, and wherein the soldered joint isformed by successive sections on the perimeter of the groove.
 6. Thebearing according to claim 2 , wherein it is the exterior edges of thecooperating faces of the collars which are beveled in order to define anexterior groove, wherein the collars are made solid by a soldered jointextending along the exterior edges of the joined-up faces, wherein theinterior edges of the co-operating faces of the collars are beveled inorder to define an interior groove, wherein the collars are also madesolid by a soldered joint extending along the interior edges of thejoined-up faces, wherein the soldered joint is formed by successivesections on the perimeter of the groove, and wherein the successivesections of the soldered joint are discontinuous.
 7. The bearingaccording to claim 1 . wherein the soldered joint is a laser solderedjoint.
 8. A process of assembly of a bearing with double ball bearingsfor the rotary support of a rotating shaft of a very high precisiondevice, wherein this bearing with double ball bearings is constituted bythe juxtaposition of two bearings with single ball bearings having twoof their respective collars, interior or exterior, tightened axiallyagainst one another, said process comprising the succession of thefollowing steps: one pairs up two bearings with single ball bearings,wherein their respective collars, interior or exterior, haveco-operating faces having complementary geometric properties, afterdismounting of the two bearings, one positions said two collars againstone another and one tightens them axially against one another with apre-determined pre-stress, one carries out soldering along at least oneof the edges, exterior or interior, of the co-operating faces of the tworespective collars under pre-stress, in such a way that the solderedjoint does not radially project beyond the peripheral annular faces ofsaid collars, then one mounts the one-piece component formed from thetwo soldered collars, under pre-stress, in position on its support organand one finishes the complete assembly of the bearing by excentrationaccording to the principle of deep-groove ball bearings.
 9. The processaccording to claim 8 , wherein said two collars are soldered along theexterior edges of their co-operating faces.
 10. The process according toclaim 9 , wherein said two collars are soldered along the interior edgesof their co-operating faces.
 11. The process according to claim 10 ,wherein said two collars are soldered with the assistance of a laserbeam.
 12. The process according to claim 11 , wherein the laser beam isguided on the interior edges of the co-operating faces of the collarssuccessively through the lights of a component of support and centeringof the collars which is positioned in the interior thereof, and whereinthe soldering is realized by successive sections.
 13. The processaccording to claim 11 , wherein the laser beam is guided on the interioredges of the co-operating faces of the collars successively through thelights of a component of support and centering of the collars which ispositioned in the interior thereof, and wherein the soldering isrealized by discontinuous successive sections.
 14. The process accordingto claim 8 , wherein the edges of the respective collars are beveled,and wherein the soldering is effected in the bottom of the groove formedby two co-operating beveled edges.
 15. The process according to claim 8, wherein the two collars are soldered along their interior and exteriorco-operating edges, and wherein the soldering of the interiorco-operating edges is carried out firstly and the soldering of theexterior co-operating edges is carried out secondly.
 16. A tool forsupporting, for coaxial centering and pre-stressing of two interiorcollars of ball bearings destined to be soldered to one another, with aview to obtaining a composite bearing, which comprises: an approximatelytubular chuck having a lateral wall with a cylindrical external face ofrevolution suitable for supporting and centering coaxially, by theirinternal faces, two interior collars positioned one after the other,first means of axial abutment, solid in respect of said chuck, againstwhich a free face of one of the two collars comes in support, andcoaxial means of tightening to said chuck, comprising second means ofaxial abutment suitable for coming to support against the free face ofthe other of the two collars, in such a way that under the effect ofsaid means of tightening, the two collars are tightened against oneanother until a pre-determined pre-stress value is obtained.
 17. Thetool according to claim 16 , which comprises a support plate of thechuck, wherein the said plate is in the form of a bowl suitable forreceiving coaxially a hub, wherein the first means of abutment areprovided on or constituted by the peripheral edge of the lateral wall ofsaid hub, and wherein the second means of abutment are provided on acover, solid in respect of said chuck, wherein the said cover is openedcentrally in order to give access to the interior of the chuck.
 18. Thetool according to claim 16 , which comprises means of rotary support ofthe chuck.
 19. The tool according to claim 16 , wherein the lateral wallof the chuck is equipped with a multiplicity of traversing lightsdistributed peripherally and in relation to which the respectiveinterior and exterior edges to be soldered of the co-operating faces ofthe two respective interior collars and exterior collars are situated,wherein each light constitutes a passage so that a laser beam crossingit can solder the edges of the collars appearing at the opening of thispassage.
 20. The tool according to claim 19 , wherein the lights of thechuck are inclined radially towards the bottom from the interior towardsthe exterior of the wall of the chuck, in order to facilitate thepositioning of the soldering laser beam approximately in the axis ofeach light.
 21. A tool for supporting, coaxial centering andpre-stressing of two exterior collars of ball bearings destined to besoldered to one another, in order to obtaining a composite bearing,which comprises: a hub, of which the lateral wall has a cylindricalinternal face of revolution suitable for supporting and centeringaxially, by their external faces, two exterior collars positioned oneafter the other, wherein the lateral wall of said hub is provided with amultiplicity of traversing lights distributed peripherally and inrelation to which the external edges to be soldered of the two collarsare situated, wherein each light constitutes a passage so that a laserbeam crossing it can solder said external edges of the two collars, anapproximately tubular chuck supported in the interior of the hub andhaving a lateral wall situated in relation to the wall of the hub, firstmeans of axial abutment, solid in respect of said hub, against which afree face of one of the two collars comes in support, and coaxial meansof tightening to said hub, comprising second means of axial abutmentsuitable for coming into support against the free face of the other ofthe two collars, in such a way that under the effect of said means oftightening, the two collars are tightened against one another until apre-determined pre-stress value is obtained.
 22. The tool according toclaim 21 , wherein the second means of abutment are solid in respect ofthe chuck and are constituted by a flank projecting radially towards theexterior starting from the upper edge of the lateral wall of said chuck.23. The tool according to claim 21 , which further comprises means ofrotary support of the chuck.
 24. The tool according to claim 21 ,wherein the lateral wall of the chuck is equipped with a multiplicity oftraversing lights distributed peripherally and in relation to which therespective interior and exterior edges to be soldered of theco-operating faces of the two respective interior collars and exteriorcollars are situated, wherein each light constitutes a passage so that alaser beam crossing it can solder the edges of the collars appearing atthe opening of this passage.
 25. The tool according to claim 24 ,wherein the lights of the chuck are inclined radially towards the bottomfrom the interior towards the exterior of the wall of the chuck, inorder to facilitate the positioning of the soldering laser beamapproximately in the axis of each light.